Method and apparatus for using gestures to control a laser tracker

ABSTRACT

Optically communicating from a user to a laser tracker a command to control tracker operation includes providing a rule of correspondence between each of a plurality of commands and temporal patterns; user selecting a first command; projecting a first light from the tracker to a retroreflector; reflecting a second light from the retroreflector that is part of the first light; obtaining first sensed data by sensing a third light imaged onto a photosensitive array that is part of the second light; user creating, between first and second times, a first temporal pattern including at least a decrease in the third light&#39;s optical power followed by an increase in its optical power, the first temporal pattern corresponding to the first command; determining the first command based at least in part on processing the first sensed data according to the rule of correspondence; and executing the first command with the tracker.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 13/803,479, filed on Mar. 14, 2013. U.S. application Ser. No.13/803,479 is a divisional application of U.S. patent application Ser.No. 13/090,889, filed on Apr. 20, 2011, which claims the benefit of U.S.Provisional Application No. 61/326,294, filed on Apr. 21, 2010, theentire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a coordinate measuring device. One setof coordinate measurement devices belongs to a class of instruments thatmeasure the three-dimensional (3D) coordinates of a point by sending alaser beam to the point, where it is intercepted by a retroreflectortarget. The instrument finds the coordinates of the point by measuringthe distance and the two angles to the target. The distance is measuredwith a distance-measuring device such as an absolute distance meter(ADM) or an interferometer. The angles are measured with anangle-measuring device such as an angular encoder. A gimbaledbeam-steering mechanism within the instrument directs the laser beam tothe point of interest. An example of such a device is a laser tracker.Exemplary laser tracker systems are described by U.S. Pat. No. 4,790,651to Brown et al., incorporated by reference herein, and U.S. Pat. No.4,714,339 to Lau et al.

A coordinate-measuring device closely related to the laser tracker isthe total station. The total station, which is most often used insurveying applications, may be used to measure the coordinates ofdiffusely scattering or retroreflective targets. Hereinafter, the termlaser tracker is used in a broad sense to include total stations.

Ordinarily the laser tracker sends a laser beam to a retroreflectortarget. A common type of retroreflector target is the sphericallymounted retroreflector (SMR), which comprises a cube-cornerretroreflector embedded within a metal sphere. The cube-cornerretroreflector comprises three mutually perpendicular mirrors. The apexof the cube corner, which is the common point of intersection of thethree mirrors, is located at the center of the sphere. It is commonpractice to place the spherical surface of the SMR in contact with anobject under test and then move the SMR over the surface being measured.Because of this placement of the cube corner within the sphere, theperpendicular distance from the apex of the cube corner to the surfaceof the object under test remains constant despite rotation of the SMR.Consequently, the 3D coordinates of a surface can be found by having atracker follow the 3D coordinates of an SMR moved over the surface. Itis possible to place a glass window on the top of the SMR to preventdust or dirt from contaminating the glass surfaces. An example of such aglass surface is shown in U.S. Pat. No. 7,388,654 to Raab et al.,incorporated by reference herein.

A gimbal mechanism within the laser tracker may be used to direct alaser beam from the tracker to the SMR. Part of the light retroreflectedby the SMR enters the laser tracker and passes onto a position detector.The position of the light that hits the position detector is used by atracker control system to adjust the rotation angles of the mechanicalazimuth and zenith axes of the laser tracker to keep the laser beamcentered on the SMR. In this way, the tracker is able to follow (track)the SMR.

Angular encoders attached to the mechanical azimuth and zenith axes ofthe tracker may measure the azimuth and zenith angles of the laser beam(with respect to the tracker frame of reference). The one distancemeasurement and two angle measurements performed by the laser trackerare sufficient to completely specify the three-dimensional location ofthe SMR.

As mentioned previously, two types of distance meters may be found inlaser trackers: interferometers and absolute distance meters (ADMs). Inthe laser tracker, an interferometer (if present) may determine thedistance from a starting point to a finishing point by counting thenumber of increments of known length (usually the half-wavelength of thelaser light) that pass as a retroreflector target is moved between thetwo points. If the beam is broken during the measurement, the number ofcounts cannot be accurately known, causing the distance information tobe lost. By comparison, the ADM in a laser tracker determines theabsolute distance to a retroreflector target without regard to beambreaks, which also allows switching between targets. Because of this,the ADM is said to be capable of “point-and-shoot” measurement.Initially, absolute distance meters were only able to measure stationarytargets and for this reason were always used together with aninterferometer. However, some modern absolute distance meters can makerapid measurements, thereby eliminating the need for an interferometer.Such an ADM is described in U.S. Pat. No. 7,352,446 to Bridges et al.,incorporated by reference herein.

In its tracking mode, the laser tracker will automatically followmovements of the SMR when the SMR is in the capture range of thetracker. If the laser beam is broken, tracking will stop. The beam maybe broken by any of several means: (1) an obstruction between theinstrument and SMR; (2) rapid movements of the SMR that are too fast forthe instrument to follow; or (3) the direction of the SMR being turnedbeyond the acceptance angle of the SMR. By default, following the beambreak, the beam remains fixed at the point of the beam break or at thelast commanded position. It may be necessary for an operator to visuallysearch for the tracking beam and place the SMR in the beam in order tolock the instrument onto the SMR and continue tracking.

Some laser trackers include one or more cameras. A camera axis may becoaxial with the measurement beam or offset from the measurement beam bya fixed distance or angle. A camera may be used to provide a wide fieldof view to locate retroreflectors. A modulated light source placed nearthe camera optical axis may illuminate retroreflectors, thereby makingthem easier to identify. In this case, the retroreflectors flash inphase with the illumination, whereas background objects do not. Oneapplication for such a camera is to detect multiple retroreflectors inthe field of view and measure each in an automated sequence. Exemplarysystems are described in U.S. Pat. No. 6,166,809 to Pettersen et al.,and U.S. Pat. No. 7,800,758 to Bridges et al., incorporated by referenceherein.

Some laser trackers have the ability to measure with six degrees offreedom (DOF), which may include three coordinates, such as x, y, and z,and three rotations, such as pitch, roll, and yaw. Several systems basedon laser trackers are available or have been proposed for measuring sixdegrees of freedom. Exemplary systems are described in U.S. PublishedPatent Application No. 2010/0128259 to Bridges, incorporated byreference herein; U.S. Pat. No. 7,800,758 to Bridges et al., U.S. Pat.No. 5,973,788 to Pettersen et al.; and U.S. Pat. No. 7,230,689 to Lau.

User Control of Laser Tracker Functionality

Two common modes of operation of the laser tracker are tracking mode andprofiling mode. In tracking mode, the laser beam from the trackerfollows the retroreflector as the operator moves it around. In profilingmode, the laser beam from the tracker goes in the direction given by theoperator, either through computer commands or manual action.

Besides these modes of operation that control the basic tracking andpointing behavior of the tracker, there are also special option modesthat enable the tracker to respond in a manner selected by the operatorahead of time. The desired option mode is typically selected in softwarethat controls the laser tracker. Such software may reside in an externalcomputer attached to the tracker (possibly through a network cable) orwithin the tracker itself. In the latter case, the software may beaccessed through console functionality built into the tracker.

An example of an option mode is the Auto Reset mode in which the laserbeam is driven to a preset reference point whenever the laser beam isbroken. One popular reference point for the Auto Reset option mode isthe tracker Home Position, which is the position of a magnetic nestmounted on the tracker body. The alternative to Auto Reset is the NoReset option mode. In this case, the laser beam continues pointing inthe original direction whenever the laser beam is broken. A descriptionof the tracker home position is given in U.S. Pat. No. 7,327,446 toCramer et al., incorporated by reference herein.

Another example of a special option mode is PowerLock, a feature offeredby Leica Geosystems on their Leica Absolute Tracker™. In the PowerLockoption mode, the location of the retroreflector is found by a trackercamera whenever the tracker laser beam is broken. The camera immediatelysends the angular coordinates of the retroreflector to the trackercontrol system, thereby causing the tracker to point the laser beam backat the retroreflector. Methods involving automatic acquisition of aretroreflector are given in international application WO 2007/079601 toDold et al. and U.S. Pat. No. 7,055,253 to Kaneko.

Some option modes are slightly more complex in their operation. Anexample is the Stability Criterion mode, which may be invoked wheneveran SMR is stationary for a given period of time. The operator may trackan SMR to a magnetic nest and set it down. If a stability criterion isactive, the software will begin to look at the stability of thethree-dimensional coordinate readings of the tracker. For instance, theuser may decide to judge the SMR to be stable if the peak-to-peakdeviation in the distance reading of the SMR is less than twomicrometers over a one second interval. After the stability criterion issatisfied, the tracker measures the 3D coordinates and the softwarerecords the data.

More complex modes of operation are possible through computer programs.For example, software is available to measure part surfaces and fitthese to geometrical shapes. Software will instruct the operator to movethe SMR over the surface and then, when finished collecting data points,to raise the SMR off the surface of the object to end the measurement.Moving the SMR off the surface not only indicates that the measurementis completed; it also indicates the position of the SMR in relation tothe object surface. This position information is needed by theapplication software to properly account for the offset caused by theSMR radius.

A second example of complex computer control is a tracker survey. In thesurvey, the tracker is driven sequentially to each of several targetlocations according to a prearranged schedule. The operator may teachthese positions prior to the survey by carrying the SMR to each of thedesired positions.

A third example of complex software control is tracker directedmeasurement. The software directs the operator to move the SMR to adesired location. It does this using a graphic display to show thedirection and distance to the desired location. When the operator is atthe desired position, the color on the computer monitor might, forexample, turn from red to green.

The element common to all tracker actions described above is that theoperator is limited in his ability to control the behavior of thetracker. On the one hand, option modes selected in the software mayenable the operator to preset certain behaviors of the tracker. However,once the option modes have been selected by the user, the behavior ofthe tracker is established and cannot be changed unless the operatorreturns to the computer console. On the other hand, the computer programmay direct the operator to carry out complicated operations that thesoftware analyzes in a sophisticated way. In either case, the operatoris limited in his ability to control the tracker and the data collectedby the tracker.

Need for Remote Tracker Commands

A laser tracker operator performs two fundamental functions. Hepositions an SMR during a measurement, and he sends commands through thecontrol computer to the tracker. However, it is not easy for oneoperator to perform both of these measurement functions because thecomputer is usually far away from the measurement location. Variousmethods have been tried to get around this limitation, but none iscompletely satisfactory.

One method sometimes used is for a single operator to set theretroreflector in place and walk back to the instrument control keyboardto execute a measurement instruction. However, this is an inefficientuse of operator and instrument time. In cases where the operator musthold the retroreflector for the measurement, single operator control isonly possible when the operator is very close to the keyboard.

A second method is to add a second operator. One operator stands by thecomputer and a second operator moves the SMR. This is obviously anexpensive method and verbal communication over large distances can be aproblem.

A third method is to equip a laser tracker with a remote control.However, remote controls have several limitations. Many facilities donot allow the use of remote controls for safety or security reasons.Even if remote controls are allowed, interference among wirelesschannels may be a problem. Some remote control signals do not reach thefull range of the laser tracker. In some situations, such as workingfrom a ladder, the second hand may not be free to operate the remotecontrol. Before a remote control can be used, it is usually necessary toset up the computer and remote control to work together, and then only asmall subset of tracker commands can ordinarily be accessed at any giventime. An example of a system based on this idea is given in U.S. Pat.No. 7,233,316 to Smith et al.

A fourth method is to interface a cell phone to a laser tracker.Commands are entered remotely by calling the instrument from the cellphone and entering numbers from the cell phone keypad or by means ofvoice recognition. This method also has many shortcomings. Somefacilities do not allow cell phones to be used, and cell phones may notbe available in rural areas. Service requires a monthly service providerfee. A cell phone interface requires additional hardware interfacing tothe computer or laser tracker. Cell phone technology changes fast andmay require upgrades. As in the case of remote controls, the computerand remote control must be set up to work together, and only a smallsubset of tracker commands can ordinarily be accessed at a given time.

A fifth method is to equip a laser tracker with internet or wirelessnetwork capabilities and use a wireless portable computer or personaldigital assistant (PDA) to communicate commands to the laser tracker.However, this method has limitations similar to a cell phone. Thismethod is often used with total stations. Examples of systems that usethis method include U.S. Published Patent Application No. 2009/017618 toKumagai et al., U.S. Pat. No. 6,034,722 to Viney et al., U.S. Pat. No.7,423,742 to Gatsios et al., U.S. Pat. No. 7,307,710 to Gatsios et al.,U.S. Pat. No. 7,552,539 to Piekutowski, and U.S. Pat. No. 6,133,998 toMonz et al. This method has also been used to control appliances by amethod described in U.S. Pat. No. 7,541,965 to Ouchi et al.

A sixth method is to use a pointer to indicate a particular location inwhich a measurement is to be made. An example of this method is given inU.S. Pat. No. 7,022,971 to Ura et al. It might be possible to adapt thismethod to give commands to a laser tracker, but it is not usually veryeasy to find a suitable surface upon which to project the pointer beampattern.

A seventh method is to devise a complex target structure containing atleast a retroreflector, transmitter, and receiver. Such systems may beused with total stations to transmit precise target information to theoperator and also to transmit global positioning system (GPS)information to the total station. An example of such a system is givenin U.S. Published Patent Application No. 2008/0229592 to Hinderling etal. In this case, no method is provided to enable the operator to sendcommands to the measurement device (total station).

An eighth method is to devise a complex target structure containing atleast a retroreflector, transmitter and receiver, where the transmitterhas the ability to send modulated light signals to a total station. Akeypad can be used to send commands to the total station by means of themodulated light. These commands are decoded by the total station.Examples of such systems are given in U.S. Pat. No. 6,023,326 toKatayama et al., U.S. Pat. No. 6,462,810 to Muraoka et al., U.S. Pat.No. 6,295,174 to Ishinabe et al., and U.S. Pat. No. 6,587,244 toIshinabe et al. This method is particularly appropriate for surveyingapplications in which the complex target and keypad are mounted on alarge staff. Such a method is not suitable for use with a laser tracker,where it is advantageous to use a small target not tethered to a largecontrol pad. Also it is desirable to have the ability to send commandseven when the tracker is not locked onto a retroreflector target.

A ninth method is to include both a wireless transmitter and a modulatedlight source on the target to send information to a total station. Thewireless transmitter primarily sends information on the angular pose ofthe target so that the total station can turn in the proper direction tosend its laser beam to the target retroreflector. The modulated lightsource is placed near the retroreflector so that it will be picked up bythe detector in the total station. In this way, the operator can beassured that the total station is pointed in the right direction,thereby avoiding false reflections that do not come from the targetretroreflector. An exemplary system based on this approach is given inU.S. Pat. No. 5,313,409 to Wiklund et al. This method does not offer theability to send general purpose commands to a laser tracker.

A tenth method is to include a combination of wireless transmitter,compass assembly in both target and total station, and guide lighttransmitter. The compass assembly in the target and total station areused to enable alignment of the azimuth angle of the total station tothe target. The guide light transmitter is a horizontal fan of lightthat the target can pan in the vertical direction until a signal isreceived on the detector within the total station. Once the guide lighthas been centered on the detector, the total station adjusts itsorientation slightly to maximize the retroreflected signal. The wirelesstransmitter communicates information entered by the operator on a keypadlocated at the target. An exemplary system based on this method is givenin U.S. Pat. No. 7,304,729 to Wasutomi et al. This method does not offerthe ability to send general purpose commands to a laser tracker.

An eleventh method is to modify the retroreflector to enable temporalmodulation to be imposed on the retroreflected light, therebytransmitting data. The inventive retroreflector comprises a cube cornerhaving a truncated apex, an optical switch attached to the front face ofthe cube corner, and electronics to transmit or receive data. Anexemplary system of this type is given in U.S. Pat. No. 5,121,242 toKennedy. This type of retroreflector is complex and expensive. Itdegrades the quality of the retroreflected light because of the switch(which might be a ferro-electric light crystal material) and because ofthe truncated apex. Also, the light returned to a laser tracker isalready modulated for use in measuring the ADM beam, and switching thelight on and off would be a problem, not only for the ADM, but also forthe tracker interferometer and position detector.

A twelfth method is to use a measuring device that contains abidirectional transmitter for communicating with a target and an activeretroreflector to assist in identifying the retroreflector. Thebidirectional transmitter may be wireless or optical and is part of acomplex target staff that includes the retroreflector, transmitter, andcontrol unit. An exemplary system of this type is described in U.S. Pat.No. 5,828,057 to Hertzman et al. Such a method is not suitable for usewith a laser tracker, where it is advantageous to use a small target nottethered to a large control pad. Also the method of identifying theretroreflector target of interest is complicated and expensive.

There is a need for a simple method for an operator to communicatecommands to a laser tracker from a distance. It is desirable that themethod be: (1) useable without a second operator; (2) useable over theentire range of the laser tracker; (3) useable without additionalhardware interfacing; (4) functional in all locations; (5) free ofservice provider fees; (6) free of security restrictions; (7) easy touse without additional setup or programming; (8) capable of initiating awide range of simple and complex tracker commands; (9) useable to call atracker to a particular target among a plurality of targets; and (10)useable with a minimum of additional equipment for the operator tocarry.

SUMMARY

According to the embodiment of the present invention, a method foroptically communicating from a user to a laser tracker, a command tocontrol operation of the laser tracker includes steps of providing arule of correspondence between each of a plurality of commands and eachof a plurality of temporal patterns, selecting by the user a firstcommand from among the plurality of commands, and projecting a firstlight from the laser tracker to a retroreflector. The method alsoincludes reflecting a second light from the retroreflector, the secondlight being a portion of the first light, and obtaining first senseddata by sensing a third light imaged onto a photosensitive array, thethird light being a portion of the second light. The method furtherincludes creating by the user, between a first time and a second time, afirst temporal pattern, the first temporal pattern including at least adecrease in optical power of the third light followed by an increase inthe optical power of the third light, the first temporal patterncorresponding to the first command. The method still further includesdetermining the first command based at least in part on processing thefirst sensed data according to the rule of correspondence, and executingthe first command with the laser tracker.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, wherein like elements are numbered alikein the several FIGURES:

FIG. 1 shows a perspective view of an exemplary laser tracker;

FIG. 2 shows computing and power supply elements attached to exemplarylaser tracker;

FIGS. 3A-3E illustrate ways in which a passive target can be used toconvey gestural information through the tracking and measuring systemsof the laser tracker;

FIGS. 4A-4C illustrate ways in which a passive target can be used toconvey gestural information through the camera system of a lasertracker;

FIGS. 5A-5D illustrate ways in which an active target can be used toconvey gestural information through the camera system of a lasertracker;

FIG. 6 is a flow chart showing the steps carried out by the operator andlaser tracker in issuing and carrying out a gestural command;

FIG. 7 is a flow chart showing the optional and required parts of agestural command;

FIGS. 8-10 show a selection of laser tracker commands and correspondinggestures that might be used by the operator to convey these commands tothe laser tracker;

FIGS. 11A-11F show alternative types of gestures that might be used;

FIG. 12 shows an exemplary command tablet for transmitting commands to alaser tracker by means of gestures;

FIG. 13 shows an exemplary method for using gestures to set a trackerreference point;

FIG. 14 shows an exemplary method for using gestures to initialize theexemplary command tablet;

FIG. 15 shows an exemplary method for using gestures to measure acircle;

FIG. 16 shows an exemplary method for using gestures to acquire aretroreflector with a laser beam from a laser tracker;

FIG. 17 shows an exemplary electronics and processing system associatedwith a laser tracker;

FIG. 18 shows an exemplary geometry that enables finding of threedimensional coordinates of a target using a camera located off theoptical axis of a laser tracker;

FIG. 19 shows an exemplary method for communicating a command to a lasertracker by gesturing with a retroreflector in a spatial pattern;

FIG. 20 shows an exemplary method for communicating a command to a lasertracker by indicating a position with a retroreflector;

FIG. 21 shows an exemplary method for communicating a command to a lasertracker by gesturing with a retroreflector in a temporal pattern;

FIG. 22 shows an exemplary method for communicating a command to a lasertracker by measuring a change in the pose of a six DOF target with a sixDOF laser tracker;

FIG. 23 shows an exemplary method for communicating a command to pointthe laser beam from the laser tracker to a retroreflector and lock ontothe retroreflector, the communication based on a gesture involving aspatial pattern created with the retroreflector;

FIG. 24 shows an exemplary method for communicating a command to pointthe laser beam from the laser tracker to a retroreflector and lock ontothe retroreflector, the communication based on a gesture involving atemporal pattern in the optical power received by the laser tracker; and

FIG. 25 shows an exemplary method for communicating a command to pointthe laser beam from the laser tracker to a retroreflector and lock ontothe retroreflector, the communication based on a gesture involving achange in the pose of a six DOF probe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An exemplary laser tracker 10 is illustrated in FIG. 1. An exemplarygimbaled beam-steering mechanism 12 of laser tracker 10 comprises zenithcarriage 14 mounted on azimuth base 16 and rotated about azimuth axis20. Payload 15 is mounted on zenith carriage 14 and rotated about zenithaxis 18. Zenith mechanical rotation axis 18 and azimuth mechanicalrotation axis 20 intersect orthogonally, internally to tracker 10, atgimbal point 22, which is typically the origin for distancemeasurements. Laser beam 46 virtually passes through gimbal point 22 andis pointed orthogonal to zenith axis 18. In other words, laser beam 46is in the plane normal to zenith axis 18. Laser beam 46 is pointed inthe desired direction by motors within the tracker (not shown) thatrotate payload 15 about zenith axis 18 and azimuth axis 20. Zenith andazimuth angular encoders, internal to the tracker (not shown), areattached to zenith mechanical axis 18 and azimuth mechanical axis 20 andindicate, to high accuracy, the angles of rotation. Laser beam 46travels to external retroreflector 26 such as the spherically mountedretroreflector (SMR) described above. By measuring the radial distancebetween gimbal point 22 and retroreflector 26 and the rotation anglesabout the zenith and azimuth axes 18, 20, the position of retroreflector26 is found within the spherical coordinate system of the tracker.

Laser beam 46 may comprise one or more laser wavelengths. For the sakeof clarity and simplicity, a steering mechanism of the sort shown inFIG. 1 is assumed in the following discussion. However, other types ofsteering mechanisms are possible. For example, it would be possible toreflect a laser beam off a mirror rotated about the azimuth and zenithaxes. An example of the use of a mirror in this way is given in U.S.Pat. No. 4,714,339 to Lau et al. The techniques described here areapplicable, regardless of the type of steering mechanism.

In exemplary laser tracker 10, cameras 52 and light sources 54 arelocated on payload 15. Light sources 54 illuminate one or moreretroreflector targets 26. Light sources 54 may be LEDs electricallydriven to repetitively emit pulsed light. Each camera 52 comprises aphotosensitive array and a lens placed in front of the photosensitivearray. The photosensitive array may be a CMOS or CCD array. The lens mayhave a relatively wide field of view, say thirty or forty degrees. Thepurpose of the lens is to form an image on the photosensitive array ofobjects within the field of view of the lens. Each light source 54 isplaced near camera 52 so that light from light source 54 is reflectedoff each retroreflector target 26 onto camera 52. In this way,retroreflector images are readily distinguished from the background onthe photosensitive array as their image spots are brighter thanbackground objects and are pulsed. There may be two cameras 52 and twolight sources 54 placed about the line of laser beam 46. By using twocameras in this way, the principle of triangulation can be used to findthe three-dimensional coordinates of any SMR within the field of view ofthe camera. In addition, the three-dimensional coordinates of the SMRcan be monitored as the SMR is moved from point to point. A use of twocameras for this purpose is described in U.S. Published PatentApplication No. 2010/0128259 to Bridges.

Other arrangements of one or more cameras and light sources arepossible. For example, a light source and camera can be coaxial ornearly coaxial with the laser beams emitted by the tracker. In thiscase, it may be necessary to use optical filtering or similar methods toavoid saturating the photosensitive array of the camera with the laserbeam from the tracker.

Another possible arrangement is to use a single camera located on thepayload or base of the tracker. A single camera, if located off theoptical axis of the laser tracker, provides information about the twoangles that define the direction to the retroreflector but not thedistance to the retroreflector. In many cases, this information may besufficient. If the 3D coordinates of the retroreflector are needed whenusing a single camera, one possibility is to rotate the tracker in theazimuth direction by 180 degrees and then to flip the zenith axis topoint back at the retroreflector. In this way, the target can be viewedfrom two different directions and the 3D position of the retroreflectorcan be found using triangulation.

A more general approach to finding the distance to a retroreflector witha single camera is to rotate the laser tracker about either the azimuthaxis or the zenith axis and observe the retroreflector with a cameralocated on the tracker for each of the two angles of rotation. Theretroreflector may be illuminated, for example, by an LED located closeto the camera. FIG. 18 shows how this procedure can be used to find thedistance to the retroreflector. The test setup 900 includes a lasertracker 910, a camera 920 in a first position, a camera 930 in a secondposition, and a retroreflector in a first position 940 and a secondposition 950. The camera is moved from the first position to the secondposition by rotating the laser tracker 910 about the tracker gimbalpoint 912 about the azimuth axis, the zenith axis, or both the azimuthaxis and the zenith axis. The camera 920 includes a lens system 922 anda photosensitive array 924. The lens system 922 has a perspective center926 through which rays of light from the retroreflectors 940, 950 pass.The camera 930 is the same as the camera 920 except rotated into adifferent position. The distance from the surface of the laser tracker910 to the retroreflector 940 is L₁ and the distance from the surface ofthe laser tracker to the retroreflector 950 is L₂. The path from thegimbal point 912 to the perspective center 926 of the lens 922 is drawnalong the line 914. The path from the gimbal point 916 to theperspective center 936 of the lens 932 is drawn along the line 916. Thedistances corresponding to the lines 914 and 916 have the same numericalvalue. As can be seen from FIG. 18, the nearer position of theretroreflector 940 places an image spot 942 farther from the center ofthe photosensitive array than the image spot 952 corresponding to thephotosensitive array 950 at the distance farther from the laser tracker.This same pattern holds true for the camera 930 located following therotation. As a result, the distance between the image points of a nearbyretroreflector 940 before and after rotation is larger than the distancebetween the image points of a far away retroreflector 950 before andafter rotation. By rotating the laser tracker and noting the resultingchange in position of the image spots on the photosensitive array, thedistance to the retroreflector can be found. The method for finding thisdistance is easily found using trigonometry, as will be obvious to oneof ordinary skill in the art.

Another possibility is to switch between measuring and imaging of thetarget. An example of such a method is described in U.S. Pat. No.7,800,758 to Bridges et al. Other camera arrangements are possible andcan be used with the methods described herein.

As shown in FIG. 2, auxiliary unit 70 is usually a part of laser tracker10. The purpose of auxiliary unit 70 is to supply electrical power tothe laser tracker body and in some cases to also supply computing andclocking capability to the system. It is possible to eliminate auxiliaryunit 70 altogether by moving the functionality of auxiliary unit 70 intothe tracker body. In most cases, auxiliary unit 70 is attached togeneral purpose computer 80. Application software loaded onto generalpurpose computer 80 may provide application capabilities such as reverseengineering. It is also possible to eliminate general purpose computer80 by building its computing capability directly into laser tracker 10.In this case, a user interface, possibly providing keyboard and mousefunctionality is built into laser tracker 10. The connection betweenauxiliary unit 70 and computer 80 may be wireless or through a cable ofelectrical wires. Computer 80 may be connected to a network, andauxiliary unit 70 may also be connected to a network. Pluralinstruments, for example, multiple measurement instruments or actuators,may be connected together, either through computer 80 or auxiliary unit70.

The laser tracker 10 may be rotated on its side, rotated upside down, orplaced in an arbitrary orientation. In these situations, the termsazimuth axis and zenith axis have the same direction relative to thelaser tracker as the directions shown in FIG. 1 regardless of theorientation of the laser tracker 10.

In another embodiment, the payload 15 is replaced by a mirror thatrotates about the azimuth axis 20 and the zenith axis 18. A laser beamis directed upward and strikes the mirror, from which it launches towarda retroreflector 26.

Sending Commands to the Laser Tracker from a Distance

FIGS. 3A-3E, 4A-4C, and 5A-5D demonstrate sensing means by which theoperator may communicate gestural patterns that are interpreted andexecuted as commands by exemplary laser tracker 10. FIGS. 3A-3Edemonstrate sensing means by which the operator communicates gesturalpatterns that exemplary laser tracker 10 interprets using its trackingand measuring systems. FIG. 3A shows laser tracker 10 emitting laserbeam 46 intercepted by retroreflector target 26. As target 26 is movedside to side, the laser beam from the tracker follows the movement. Atthe same time, the angular encoders in tracker 10 measure the angularposition of the target in the side-to-side and up-down directions. Theangular encoder readings form a two dimensional map of angles that canbe recorded by the tracker as a function of time and analyzed to lookfor patterns of movement.

FIG. 3B shows laser beam 46 tracking retroreflector target 26. In thiscase, the distance from tracker 10 to target 26 is measured. The ADM orinterferometer readings form a one-dimensional map of distances that canbe recorded by tracker 10 as a function of time and analyzed to look forpatterns of movement. The combined movements of FIGS. 3A and 3B can alsobe evaluated by laser tracker 10 to look for a pattern inthree-dimensional space.

The variations in angle, distance, or three-dimensional space may all beconsidered as examples of spatial patterns. Spatial patterns arecontinually observed during routine laser tracker measurements. Withinthe possible range of observed patterns, some patterns may haveassociated laser tracker commands. There is one type of spatial patternin use today that may be considered a command. This pattern is amovement away from the surface of an object following a measurement. Forexample, if an operator measures a number of points on an object with anSMR to obtain the outer diameter of the object and then moves the SMRaway from the surface of the object, it is clear that an outer diameterwas being measured. If an operator moves the SMR away from the surfaceafter measuring an inner diameter, it is clear that the inner diameterwas being measured. Similarly, if an operator moves an SMR upward aftermeasuring a plate, it is understood that the upper surface of the platewas being measured. It is important to know which side of an object ismeasured because it is necessary to remove the offset of the SMR, whichis the distance from the center to the outer surface of the SMR. If thisaction of moving the SMR away from an object is automaticallyinterpreted by software associated with the laser tracker measurement,then the movement of the SMR may be considered to be a command thatindicates “subtract the SMR offset away from the direction of movement.”Therefore, after including this first command in addition to othercommands based on the spatial patterns, as described herein, there is aplurality of commands. In other words, there is a correspondence betweena plurality of tracker commands and a plurality of spatial patterns.

With all of the discussions in the present application, it should beunderstood that the concept of a command for a laser tracker is to betaken within the context of the particular measurement. For example, inthe above situation in which a movement of the retroreflector was saidto indicate whether the retroreflector target was measuring an inner orouter diameter, this statement would only be accurate in the context ofa tracker measuring an object having a circular profile.

FIG. 3C shows laser beam 46 tracking retroreflector target 26. In thiscase, retroreflector target 26 is held fixed, and tracker 10 measuresthe three-dimensional coordinates. Certain locations within themeasurement volume may be assigned special meanings, as for example whena command tablet, described later, is located at a particularthree-dimensional position.

FIG. 3D shows laser beam 46 being blocked from reaching retroreflectortarget 26. By alternately blocking and unblocking laser beam 46, thepattern of optical power returned to tracker 10 is seen by the trackermeasurement systems, including the position detector and the distancemeters. The variation in this returned pattern forms a pattern as afunction of time that can be recorded by the tracker and analyzed tolook for patterns.

A pattern in the optical power returned to the laser tracker is oftenseen during routine measurements. For example, it is common to block alaser beam from reaching a retroreflector and then to recapture thelaser beam with the retroreflector at a later time, possibly aftermoving the retroreflector to a new distance from the tracker. Thisaction of breaking the laser beam and then recapturing the laser beammay be considered to be a simple type of user command that indicatesthat the retroreflector is to be recaptured after it is moved to a newposition. Therefore, after including this first simple command inaddition to other commands based on the temporal variation in opticalpower, as described herein, there is a plurality of commands. In otherwords, there is a correspondence between a plurality of tracker commandsand a plurality of patterns based on variations in optical powerreceived by a sensor disposed on the laser tracker.

A change in optical power is often seen during routine measurements whenthe laser beam is blocked from returning to the laser tracker. Such anaction may be interpreted as a command that indicates “stop tracking” or“stop measuring.” Similarly, a retroreflector may be moved to intercepta laser beam. Such simple actions might be interpreted as commands thatindicates “start tracking.” These simple commands are not of interest inthe present patent application. For this reason, commands discussedherein involve changes in optical power that include at least a decreasein optical power followed by an increase in optical power.

FIG. 3E shows laser beam 46 tracking retroreflector 26 with a sixdegree-of-freedom (DOF) probe 110. Many types of six-DOF probes arepossible, and the six-DOF probe 110 shown in FIG. 3E is merelyrepresentative, and not limiting in its design. Tracker 10 is able tofind the angle of angular tilt of the probe. For example, the trackermay find and record the roll, pitch, and yaw angles of probe 110 as afunction of time. The collection of angles can be analyzed to look forpatterns.

FIGS. 4A-4C demonstrate sensing means by which the operator maycommunicate gestural patterns that exemplary laser tracker 10 interpretsusing its camera systems. FIG. 4A shows cameras 52 observing themovement of retroreflector target 26. Cameras 52 record the angularposition of target 26 as a function of time. These angles are analyzedlater to look for patterns. It is only necessary to have one camera tofollow the angular movement of retroreflector target 26, but the secondcamera enables calculation of the distance to the target. Optional lightsources 54 illuminate target 26, thereby making it easier to identify inthe midst of background images. In addition, light sources 54 may bepulsed to further simplify target identification.

FIG. 4B shows cameras 52 observing the movement of retroreflector target26. Cameras 52 record the angular positions of target 26 and, usingtriangulation, calculate the distance to target 26 as a function oftime. These distances are analyzed later to look for patterns. Optionallight sources 54 illuminate target 26.

FIG. 4C shows cameras 52 observing the position of retroreflector target26, which is held fixed. Tracker 10 measures the three-dimensionalcoordinates of target 26. Certain locations within the measurementvolume may be assigned special meanings, as for example when a commandtablet, described later, is located at a particular three-dimensionalposition.

FIGS. 5A-5D demonstrate sensing means by which the operator maycommunicate gestural patterns that exemplary laser tracker 10 interpretsby using its camera systems in combination with an active light source.FIG. 5A shows cameras 52 observing active retroreflector target 120.Active retroreflector target comprises retroreflector target 126 ontowhich are mounted light source 122 and control button 124 that turnslight source 122 on and off. The operator presses control button 124 onand off in a prescribed pattern to illuminate light source 122 in apattern that is seen by cameras 52 and analyzed by tracker 10.

An alternative mode of operation for FIG. 5A is for the operator to holddown control button 124 only while gesturing a command, which might begiven, for example, using side-to-side and up-down movements. By holdingdown control button 124 only during this time, parsing and analysis issimplified for tracker 10. There are several ways that the tracker canobtain the pattern of movement, whether control button 124 is held downor not: (1) cameras 52 can follow the movement of light source 122; (2)cameras 52 can follow the movement of retroreflector 126, which isoptionally illuminated by light sources 54; or (3) tracking andmeasurement systems of laser tracker 10 can follow the movement ofretroreflector 126. In addition, it is possible for the tracker tofollow retroreflector 126 in order to collect measurement data while theoperator is at the same time pressing control button 124 up and down toproduce a temporal pattern in the emitted LED light to issue a commandto the tracker.

FIG. 5B shows cameras 52 observing light source 132 on six DOF probe130. Six-DOF probe 130 comprises retroreflector 136, light source 132,and control button 134. The operator presses control button 134 on andoff in a prescribed manner to illuminate light source 132 in a patternseen by cameras 54 and analyzed by tracker 10.

An alternative mode of operation for FIG. 5B is for the operator to holddown control button 134 only while gesturing a command, which might begiven, for example, using side-to-side and up-down movements orrotations. By holding down control button 134 only during this time,parsing and analysis is simplified for tracker 10. In this case, thereare several ways that the tracker can obtain the pattern of movement:(1) cameras 52 can follow the movement of light source 132; (2) cameras52 can follow the movement of retroreflector 136, which is optionallyilluminated by light sources 54; or (3) tracking and measurement systemsof laser tracker 10 can follow the movement or rotation of six-DOFtarget 130.

FIGS. 5A, 5B can also be used to indicate a particular position. Forexample, a point on the spherical surface of the active retroreflectortarget 120 or a point on the spherical surface of the six-DOF probe 130can be held against an object to provide a location that can bedetermined by the cameras 52. Certain locations within the measurementvolume may be assigned special meanings, as for example when a commandtablet, described in reference to FIG. 12, is located at a particularthree-dimensional position.

FIG. 5C shows cameras 52 observing light source 142 on wand 140. Wand140 comprises light source 142 and control button 144. The operatorpresses control button 144 on and off in a prescribed manner toilluminate light source 142 in a temporal pattern seen by cameras 54 andanalyzed by tracker 10.

FIG. 5D shows cameras 52 observing light source 142 on wand 140. Theoperator presses control button 144 on wand 140 to continuouslyilluminate light source 142. As the operator moves wand 140 in anydirection, cameras 52 record the motion of wand 140, the pattern ofwhich is analyzed by tracker 10. It is possible to use a single camera52 if only the pattern of the transverse (side-to-side, up-down)movement and not the radial movement is important.

As explained above, tracker 10 has the ability to detect spatialpositions, spatial patterns, and temporal patterns created by theoperator through the use of retroreflector target 26, six-DOF target 110or 130, active retroreflector target 120, or wand 140. These spatial ortemporal patterns are collectively referred to as gestures. Theparticular devices and modes of sensing depicted in FIGS. 3A-3E, 4A-4C,5A-5D are specific examples and should not be understood to limit thescope of the invention.

FIG. 6 shows flow chart 200, which lists steps carried out by theoperator and laser tracker 10 in issuing and carrying out gesturalcommands. In step 210, laser tracker 10 scans continuously for commands.In other words, the tracker uses one or more of the modes of sensingshown in FIGS. 3A-3E, 4A-4C, 5A-5D to record positions, spatialpatterns, and temporal patterns. In step 220, the operator signals acommand. This means that the operator creates a gesture by taking asuitable action on an object such as retroreflector target 26, six-DOFtarget 110 or 130, active retroreflector target 120, or wand 140. Anappropriate action might involve movement to a particular absolutecoordinate or movement to create a particular spatial or temporalpattern.

In step 230, tracker 10 intercepts and parses the command just signaledby the operator. It intercepts the command by sensing and recordingspatial and temporal information from the moving objects. It parses thecommand by using computing power, possibly within the tracker, to breakthe stream of data into appropriate subunits and identify the patternsformed by the subunits according to an algorithm. Types of algorithmsthat might be used are discussed hereinafter.

In step 240, the tracker acknowledges that a command has been received.The acknowledgement might be in the form of a flashing light located onthe tracker, for example. The acknowledgement might take several formsdepending on whether the command was clearly received, garbled orincomplete, or impossible to carry out for some reason. The signal foreach of these different conditions could be given in a variety ofdifferent ways. For example, different colors of lights, or differentpatterns or durations of flashes might be possible. Audible tones couldalso be used as feedback.

In step 250, tracker 10 checks whether the command is garbled. In otherwords, is the meaning of the received command unclear? If the command isgarbled, the flow returns to step 210, where tracker 10 continues toscan for commands. Otherwise the flow continues to step 260, wheretracker 10 checks whether the command is incomplete. In other words, ismore information needed to fully define the command? If the command isincomplete, the flow returns to step 210, where tracker 10 continues toscan for commands. Otherwise the flow continues to step 270.

In step 270, tracker 10 executes whatever actions are required by thecommand. In some cases, the actions require multiple steps both on thepart of the tracker and the operator. Examples of such cases arediscussed below. In step 280, tracker 10 signals that the measurement iscomplete. The flow then returns to step 210, where the tracker continuesto scan for commands.

FIG. 7 shows that step 220, in which the operator signals a command,comprises three steps: step 222—prologue, step 224—directive, and step226—epilogue. The prologue and epilogue steps are optional. Thedirective part of the command is that part of the command that conveysthe instructions to be followed. The prologue part of the commandindicates to the tracker that the command is starting and the directivewill soon be given. The epilogue part of the command indicates to thetracker that the command is over.

FIGS. 8-10 show two exemplary sets of gestures (“Example 1 gesture” and“Example 2” gesture) that correspond to an exemplary set of commands.The leftmost columns of FIGS. 8-10 show the exemplary set of commands.Some of these commands are taken from FARO CAM2 software. Other commandsare taken from other software such as SMX Insight software or theUtilities software shipped with the FARO laser tracker. Besides theseexamples, commands may be taken from other software or simply createdfor a particular need. In each of FIGS. 8-10, the second column shows asoftware shortcut in the CAM2 software, if available. An operator maypress this software shortcut on the keyboard to execute thecorresponding command. The third and fourth columns of FIGS. 8-10 showsome spatial patterns that might be used to represent a certain command.The two dimensional spatial patterns might be sensed using methods shownin FIG. 3A, 4A, or 5D, for example.

For each of the gestures in the third and fourth columns in FIGS. 8-10,the starting position is indicated with a small circle and the endingposition is indicated with an arrow. The gestures in the third column ofFIGS. 8-10 are simple shapes—circles, triangles, or squares. The 28shapes shown in this column are distinguished from one another by theirorientations and starting positions. In contrast, the shapes in thefourth column of FIGS. 8-10 are suggestive of the command to be carriedout. The main advantage of the shapes in the third columns is that theseare easier for the computer to recognize and interpret as commands. Thisaspect is discussed in more detail below. The main advantage of theshapes in the fourth columns is that these may be easier for theoperator to remember.

FIGS. 11A-11F show some alternative spatial patterns that might be usedin gestures. FIG. 11A shows single strokes; FIG. 11B shows alphanumericcharacters; FIG. 11C shows simple shapes; FIG. 11D shows a simple pathwith the path retraced or repeated once; FIG. 11E shows a compound pathformed of two or more simpler patterns; and FIG. 11F shows patternsformed of two or more letters.

FIG. 12 shows an exemplary command tablet 300. The operator carriescommand tablet 300 to a convenient location near the position where themeasurement is being made. Command tablet 300 may be made of stiffmaterial having the size of a sheet of notebook paper or larger. Theoperator places command tablet 300 on a suitable surface and may use avariety of means to hold the target in place. Such means may includetape, magnets, hot glue, tacks, or Velcro. The operator establishes thelocation of command tablet 300 with the frame of reference of lasertracker 10 by touching fiducial positions 310, 312, and 314 withretroreflector 26. It would be possible to use multiple command tabletsin a given environment. An exemplary procedure for finding the commandtablet location is discussed below.

Command tablet 300 may be divided into a number of squares. In additionto the squares for fiducial positions 310, 312, and 314, there aresquares for commands in FIGS. 8-10, and other squares corresponding totarget type, nest type, direction, and number. The layout and contentsof exemplary command tablet 300 is merely suggestive, and the commandtablet may be effectively designed in a wide variety of ways. A customcommand tablet may also be designed for a particular job.

To gesture a command to laser tracker 10, the operator touches theretroreflector to the desired square on command tablet 300. This actionby the operator corresponds to step 220 in FIG. 200. Sensing of theaction may be carried out by methods shown in FIG. 3C or 4C, forexample. If a sequence involving multiple numbers is to be entered—forexample, the number 3.50—then the squares 3, point, 5, and 0 would betouched in order. As is discussed below, there are various ways ofindicating to the tracker that a square is to be read. One possibilityis to wait a preset time—say, for at least two seconds. The tracker willthen give a signal, which might be a flashing light, for example,indicating that it has read the contents of the square. When the entiresequence of numbers has been entered, the operator may terminate thesequence in a predetermined way. For example, the agreed upon terminatormight be to touch one of the fiducial points.

Command tablet 300 may also be used with an articulated arm CMM insteadof a laser tracker. An articulated arm CMM comprises a number of jointedsegments attached to a stationary base on one end and a probe, scanner,or sensor on the other end. Exemplary articulated arm CMMs are describedin U.S. Pat. No. 6,935,036 to Raab et al., which is incorporated byreference herein, and U.S. Pat. No. 6,965,843 to Raab et al., which isincorporated by reference herein. The probe tip is brought into contactwith the squares of command tablet 300 in the same way as theretroreflector target is brought into contact with the squares ofcommand tablet 300 when using a laser tracker. An articulated arm CMMtypically makes measurement over a much smaller measurement volume thandoes a laser tracker. For this reason, it is usually easy to find aconvenient place to mount command tablet 300 when using an articulatedarm CMM. The particular commands included in command tablet 300 would beadapted to commands appropriate for the articulated arm CMM, which aredifferent than commands for the laser tracker. The advantage of using acommand tablet with an articulated arm CMM is that it saves the operatorthe inconvenience and lost time of setting down the probe, moving to thecomputer, and entering a command before returning to the articulated armCMM.

We now give four examples in FIGS. 13-16 of how gestures may be used.FIG. 13 shows gestures being used to set a reference point for exemplarylaser tracker 10. Recall from the earlier discussion that Auto Reset isa possible option mode of a laser tracker. If the laser tracker is setto the Auto Reset option, then whenever the beam path is broken, thelaser beam will be directed to the reference position. A popularreference position is the home position of the tracker, whichcorresponds to the position of a magnetic nest permanently mounted onthe body of the laser tracker. Alternatively, a reference point close tothe work volume may be chosen to eliminate the need for the operator towalk back to the tracker when the beam is broken. (Usually thiscapability is most important when the tracker is using an interferometerrather than an ADM to make the measurement.)

In FIG. 13, the actions shown in flow chart 400 are carried out to set areference point through the use of gestures. In step 420, the operatormoves the target in the pattern shown for “Set Reference Point” in FIG.10. The target in this case may be retroreflector 26, for example, asshown in FIG. 3A. In step 430, laser tracker 10 intercepts and parsesthe command and acknowledges that the command has been received. In thiscase, the form of acknowledgement is two flashes of the red light on thetracker front panel. However, other feedback such as a different coloror pattern, or an audible tone may be used. In step 440, the operatorplaces SMR 26 into the magnetic nest that defines the referenceposition. Laser tracker 10 continually monitors position data of SMR 26and notes when it is stationary. If the SMR is stationary for fiveseconds, tracker 10 recognizes that the operator has intentionallyplaced the SMR in the nest, and the tracker begins to measure. A redlight on the tracker panel, for example, may be illuminated while themeasurement is taking place. The red light goes out when the measurementis completed.

In FIG. 14, the actions shown in flow chart 500 are carried out toestablish the position of exemplary command tablet 300 inthree-dimensional space. Recall from the earlier discussion that commandtablet 300 has three fiducial positions 310, 312, and 314. By touching aretroreflector target to these three positions, the position of commandtablet 300 in three-dimensional space can be found. In step 510, theoperator moves the target in the pattern shown for “Initialize CommandTablet” in FIG. 9. The target in this case may be retroreflector 26, forexample, as shown in FIG. 3A. In step 520, laser tracker 10 interceptsand parses the command and acknowledges that the command has beenreceived by flashing the red light twice. In step 530, the operatorholds SMR 26 against one of the three fiducial points. Laser tracker 10continually monitors position data of SMR 26 and notes when the SMR isstationary. In step 540, if SMR 26 is stationary for five seconds,tracker 10 measures the position of SMR 26. In step 550, the operatorholds SMR 26 against a second of the three fiducial points. In step 560,if SMR 26 is stationary for five seconds, tracker 10 measures theposition of SMR 26. In step 570, the operator holds SMR 26 against thethird of the three fiducial points. In step 580, if SMR 26 is stationaryfor five seconds, tracker 10 measures the position of SMR 26. Nowtracker 10 knows the three-dimensional positions of each of the threefiducial points, and it can calculate the distance between these threepairs of points from these three points. In step 590, tracker 10searches for an error by comparing the known distances between thepoints to the calculated distances between the points. If thedifferences are too large, a signal error is indicated in step 590 by asuitable indication, which might be flashing of the red light for fiveseconds.

In FIG. 15, the actions shown in flow chart 600 are carried out tomeasure a circle through the use of gestures. In step 610, the operatormoves the target in the pattern shown for “Measure a Circle” in FIG. 8.The target in this case may be retroreflector 26, for example, as shownin FIG. 3A. In step 620, laser tracker 10 intercepts and parses thecommand and acknowledges that the command has been received by flashingthe red light twice. In step 630, the operator holds retroreflector 26against the workpiece. For example, if the operator is measuring theinside of a circular hole, he will place the SMR against the part on theinside of the hole. Laser tracker 10 continually monitors position dataof retroreflector 26 and notes when the SMR is stationary. In step 640,after retroreflector 26 is stationary for five seconds, the red lightcomes on and tracker 10 commences continuous measurement of the positionof retroreflector 26. In step 650, the operator moves retroreflector 10along the circle of interest. In step 660, when enough points have beencollected, the operator moves retroreflector 26 away from the surface ofthe object being measured. The movement of retroreflector 26 indicatesthat the measurement is complete. It also indicates whetherretroreflector target 26 is measuring an inner diameter or outerdiameter and enables the application software to remove an offsetdistance to account for the radius of retroreflector 26. In step 670,tracker 10 flashes the red light twice to indicate that the requiredmeasurement data has been collected.

In FIG. 16, the actions shown in flow chart 700 are carried out toacquire a retroreflector after the laser beam from laser tracker 10 hasbeen broken. In step 710, the operator moves the retroreflector in thepattern shown for “Acquire SMR” in FIG. 10. The target in this case maybe retroreflector 26, for example, as shown in FIG. 4A. At the beginningof this procedure, the SMR has not acquired the SMR and hence the modesshown in FIGS. 3A-3E cannot be used. Instead cameras 52 and lightsources 54 are used to locate retroreflector 26. In step 720, lasertracker 10 intercepts and parses the command and acknowledges that thecommand has been received by flashing the red light twice. At the sametime, it drives the laser beam 46 toward the center of retroreflector26. In step 730, tracker 10 checks whether the laser beam has beencaptured by retroreflector 26. In most cases, the laser beam is drivenclose enough to the center of retroreflector 26 that it lands within theactive area of the position detector within the tracker. In this case,the tracker servo system drives the laser beam in a direction that movesthe laser beam toward the center of the position detector, which alsocauses the laser beam to move to the center of retroreflector 26. Normaltracking occurs thereafter. If the laser beam is not driven close enoughto the center of retroreflector 26 to land on the position detectorwithin the tracker, then one possibility is to perform a spiral search,as shown in step 740. Laser tracker 10 carries out a spiral search byaiming the laser beam in a starting direction and then directing thebeam in an ever widening spiral. Whether or not to perform a spiralsearch can be set as an option with the laser tracker or the applicationsoftware used with the laser tracker. Another option, which might beappropriate for a rapidly moving target, is to repeat step 720repeatedly until the laser beam is captured by the retroreflector oruntil there is a timeout.

As discussed previously with reference to FIG. 7, the operator signals acommand through the use of three steps: an optional prologue, adirective, and an optional epilogue. If tracker 10 is constantly parsingdata and can quickly respond when the desired pattern has been produced,then it may be possible to use the directive alone without the prologueor epilogue. Similarly, if the operator touches a position on commandtablet 300, the command should be clear to the tracker without the needfor a prologue or epilogue. On the other hand, if the tracker cannotparse quickly enough to respond immediately to the patterns created bythe operator, or if there is a chance that the operator might create acommand pattern unintentionally, then use of a prologue, epilogue, orboth may be needed.

An example of a simple prologue or epilogue is simply a pause in themovement of the target, which might be any of the targets shown in FIGS.3A-3E, 4A-4C, and 5A-5D. For example, the operator may pause for one ortwo seconds before the start of a pattern and one or two seconds at theend of the pattern. By pausing in this way, the starting and endingpositions of each gesture, indicated by circles and arrows,respectively, in FIGS. 8-10 and by circles and squares, respectively, inFIG. 11 will be more easily understood by the parsing software withinthe tracker or computer.

Another example of a simple prologue or epilogue is rapid blocking andunblocking of the laser beam from the tracker. For example, the operatormay splay his fingers so that there is a space between each of the fourdigits. Then by moving his fingers rapidly across the laser beam, thebeam will be broken and unbroken four times in rapid succession. Such atemporal pattern, which might be referred to as the “four fingersalute”, is readily recognized by the laser tracker. The modes ofsensing based on temporal variations in returned laser power are shownin FIG. 3D with a passive target and in FIGS. 5A-5C with active targets.

Besides the use of a prologue or epilogue in the gestural command, atype of prologue is also sometimes needed at the start of an action bythe laser tracker. For example, in the examples of FIGS. 13-15, there isa wait of five seconds after a command is given before the trackermeasurement is made. The purpose of this wait is to give the operatortime to get the retroreflector target into position before beginning themeasurement. Of course, the time of five seconds is arbitrary and couldbe set to any desired value. In addition, it would be possible to useother indicators that the measurement should begin. For example, itwould be possible to use a four-finger salute rather than a time delayto indicate readiness for measurement.

Active targets such as those shown in FIGS. 5A-D are useful inapplications such as tool building and device assembly. A tool is a typeof apparatus made to assist in the manufacture of other devices. Infields such as automotive and aerospace manufacturing, tools areconstructed to exacting specifications. The laser tracker helps both inassembling and in checking such tools. In many cases, it is necessary toalign the component elements of a tool with respect to one another. Asingle retroreflector target, such as retroreflector 26, can be used toestablish a coordinate system to which each element in the tool can beproperly aligned. In a complicated tool, however, this can involve a lotof iterative measuring. An alternative is to mount multipleretroreflector targets on the tooling elements and then measure all ofthese in rapid succession. Such rapid measurement is made possible todayby modern tracker technologies such as absolute distance meters andcamera systems (such as components 42, 44). If multiple retroreflectorsare mounted directly on tooling, then it may be difficult or inefficientfor an operator to use one of these retroreflectors to create gesturalcommands. It may be more convenient to use a wand such as 140 shown inFIG. 5C or 5D. The operator can quickly give commands using a wandwithout disturbing the retroreflectors mounted on the tooling. Such awand may be mounted on the end of a hammer or similar device to leavethe operator's hands free to perform assembly and adjustment. In somecases, a separate retroreflector or six-DOF probe, like those shown inFIGS. 5A and 5B, respectively, may be needed during tool building. Byadding a light source and control button to the basic SMR or six-DOFprobe, the operator can issue commands in a very flexible way.

Active targets such as those shown in FIGS. 5A-D are also useful indevice assembly. A modern trend is flexible assembly using lasertrackers rather than automated tooling assembly. An important advantageof the tracker approach is that little advance preparation is required.One thing that makes such assembly practical today is the availabilityof software that matches CAD software drawings to measurements made bylaser trackers. By placing retroreflectors on the parts to be assembledand then sequentially measuring the retroreflectors with a lasertracker, the closeness of assembly can be shown on a computer displayusing colors such as red to indicate “far away”, yellow to indicate“getting closer”, and green to indicate “close enough”. Using an activetarget, the operator can give commands to measure selected targets orgroups of targets in ways to optimize the assembly process.

Multiple retroreflectors are often located in a single measurementvolume. Examples for tool building and device assembly with multipleretroreflectors were described above. These examples showed that anactive target can be particularly useful. In other cases, the ability ofthe laser tracker to recognize movements of multiple passiveretroreflectors can be useful. For example, suppose that multipleretroreflectors have been placed on a tooling fixture such as a sheetmetal stamping press and the operator wants to perform a target surveyafter each operation of the fixture. The survey will sequentiallymeasure the coordinates of each target to check the repeatability of thetooling fixture. An easy way for the operator to set up the initialsurvey coordinates is to sequentially lift each retroreflector out ofits nest and move it around according to a prescribed gestural pattern.When the tracker recognizes the pattern, it measures the coordinates ofthe retroreflector in its nest. It is the ability of the tracker camerasto recognize gestural patterns over a wide field of view that enablesthe operator to conveniently switch among retroreflectors.

As mentioned previously, there are several different types of methods oralgorithms that can be used to identify gestural patterns and interpretthese as commands. Here we suggest a few methods, while recognizing thata wide variety of methods or algorithms could be used and would workequally well. As explained earlier, there are three main types ofpatterns of interest: (1) single-point absolute position, (2) temporalpatterns, and (3) movement patterns. Recognizing single-point absoluteposition is arguably the easiest of these three categories. In thiscase, the tracker simply needs to compare measured coordinates to seewhether these agree to within a specified tolerance to a coordinate onthe surface of command tablet 300.

Temporal patterns are also relatively easy to identify. A particularpattern might consist of a certain number of on-off repetitions, forexample, and additional constraints may be placed on the allowable onand off times. In this case, tracker 10 simply needs to record the onand off times and periodically check whether there is a match with apre-established pattern. It would of course be possible to reduce thepower level rather than completely extinguishing the light to send asignal to the tracker. Reduction in the level of retroreflected laserpower could be obtained by many means such as using a neutral densityfilter, polarizer, or iris.

Movement patterns may be parsed in one, two, or three dimensions. Achange in radial distance is an example of a one-dimensional movement. Achange in transverse (up-down, side-to-side) movement is an example oftwo-dimensional measurement. A change in radial and transversedimensions is an example of three-dimensional measurement. Of course,the dimensions of interest are those currently monitored by the lasertracker system. One way to help simplify the parsing and recognitiontask is to require that it occur within certain bounds of time andspace. For example, the pattern may be required to be between 200 mm and800 mm (eight inches and 32 inches) in extent and to be completed inbetween one and three seconds. In the case of transverse movements, thetracker will note the movements as changes in angles, and these anglesin radians must be multiplied by the distance to the target to get thesize of the pattern. By restricting the allowable patterns to certainbounds of time and space, many movements can be eliminated from furtherconsideration as gestural commands. Those that remain may be evaluatedin many different ways. For example, data may be temporarily stored in abuffer that is evaluated periodically to see whether a potential matchexists to any of the recognized gestural patterns. A special case of agestural movement pattern that is particularly easy to identify is whenthe command button 124 in FIG. 5A is pushed to illuminate light 122 toindicate that a gesture is taking place. The computer then simply needsto record the pattern that has taken place when light 122 wasilluminated and then evaluate that pattern to see whether a validgesture has been generated. A similar approach can be taken when theoperator presses command button 134 to illuminate light 132 in FIG. 5Bor presses command button 144 to illuminate light 142 in FIG. 5D.

Besides these three main patterns, it is also possible to createpatterns made using a passive object or a passive object in combinationwith a retroreflector. For example, the cameras on the tracker mightrecognize that a particular command is given whenever a passive redsquare of a certain size is brought within one inch of the SMR.

It would also be possible to combine two of the three main patterns. Forexample, it would be possible to combine both the speed of movement witha particular spatial pattern, thereby combining pattern types two andthree. As another example, the operator may signal a particular commandwith a saw tooth pattern comprising a rapid movement up, followed by aslow return. Similarly acceleration might be used. For example, a flickmotion might be used to “toss” a laser beam away in a particulardirection around an object.

Variations are also possible within types of patterns. For example,within the category of spatial patterns, it would be possible todistinguish between small squares (say, three-inches on a side) andlarge squares (say, 24 inches on a side).

The methods of algorithms discussed above are implemented by means ofprocessing system 800 shown in FIG. 17. Processing system 800 comprisestracker processing unit 810 and optionally computer 80. Processing unit810 includes at least one processor, which may be a microprocessor,digital signal processor (DSP), field programmable gate array (FPGA), orsimilar device. Processing capability is provided to process informationand issue commands to internal tracker processors. Such processors mayinclude position detector processor 812, azimuth encoder processor 814,zenith encoder processor 816, indicator lights processor 818, ADMprocessor 820, interferometer (IFM) processor 822, and camera processor824. It may include gestures preprocessor 826 to assist in evaluating orparsing of gestures patterns. Auxiliary unit processor 870 optionallyprovides timing and microprocessor support for other processors withintracker processor unit 810. It may communicate with other processors bymeans of device bus 830, which may transfer information throughout thetracker by means of data packets, as is well known in the art. Computingcapability may be distributed throughout tracker processing unit 810,with DSPs and FPGAs performing intermediate calculations on datacollected by tracker sensors. The results of these intermediatecalculations are returned to auxiliary unit processor 870. As explainedpreviously, auxiliary unit 70 may be attached to the main body of lasertracker 10 through a long cable, or it may be pulled within the mainbody of the laser tracker so that the tracker attaches directly (andoptionally) to computer 80. Auxiliary unit 870 may be connected tocomputer 80 by connection 840, which may be an Ethernet cable orwireless connection, for example. Auxiliary unit 870 and computer 80 maybe connected to the network through connections 842, 844, which may beEthernet cables or wireless connections, for example.

Preprocessing of sensor data may be evaluated for gestures content byany of processors 812-824, but there may also be a processor 826specifically designated to carry out gestures preprocessing. Gesturespreprocessor 826 may be a microprocessor, DSP, FPGA, or similar device.It may contain a buffer that stores data to be evaluated for gesturescontent. Preprocessed data may be sent to auxiliary unit for finalevaluation, or final evaluation of gestures content may be carried outby gestures preprocessor 826. Alternatively, raw or preprocessed datamay be sent to computer 80 for analysis.

Although the use of gestures described above has mostly concentrated ontheir use with a single laser tracker, it is also beneficial to usegestures with collections of laser trackers or with laser trackerscombined with other instruments. One possibility is to designate onelaser tracker as the master that then sends commands to otherinstruments. For example, a set of four laser trackers might be used ina multilateration measurement in which three-dimensional coordinates arecalculated using only the distances measured by each tracker. Commandscould be given to a single tracker, which would relay commands to theother trackers. Another possibility is to allow multiple instruments torespond to gestures. For example, suppose that a laser tracker were usedto relocate an articulated arm CMM. An example of such a system is givenin U.S. Pat. No. 7,804,602 to Raab, which is incorporated by referenceherein. In this case, the laser tracker might be designated as themaster in the relocation procedure. The operator would give gesturalcommands to the tracker, which would in turn send appropriate commandsto the articulated arm CMM. After the relocation procedure wascompleted, the operator could use a command tablet to give gesturalcommands to the articulated arm CMM, as described above.

FIG. 19 shows steps 1900 that are carried out in giving a gesture tocommunicate a command to the laser tracker according to the discussionsthat referenced FIGS. 3A-B, 4A-B, and 5A. Step 1910 is to provide a ruleof correspondence between commands and spatial patterns. Step 1920 isfor the user to select a command from among the possible commands. Step1930 is for the user to move the retroreflector in a spatial patterncorresponding to the desired command. The spatial pattern might be intransverse or radial directions. Step 1940 is to project a light fromthe laser tracker to the retroreflector. This light may be a beam oflight emitted along the optical axis of the laser tracker or it may belight emitted by an LED near a camera disposed on the laser tracker.Step 1950 is to reflect light from the retroreflector back to the lasertracker. Step 1960 is to sense the reflected light. The sensing may bedone by a photosensitive array within a camera disposed on the tracker;by a position detector in the tracker, or by a distance meter within thetracker. Step 1970 is to determine the command based on the rule ofcorrespondence. Step 1980 is to execute the command.

FIG. 20 shows steps 2000 that are carried out in giving a gesture tocommunicate a command to the laser tracker according to the discussionsthat referenced FIGS. 3C, 4C, and 5A. Step 2010 is to provide a rule ofcorrespondence between commands and three-dimensional positions. Step2020 is for the user to select a command from among the possiblecommands. Step 2030 is for the user to move the retroreflector to aposition corresponding to the desired command, possibly by bringing theretroreflector target in contact with a command tablet. Step 2040 is toproject a light from the laser tracker to the retroreflector. This lightmay be a beam of light emitted along the optical axis of the lasertracker or it may be light emitted by an LED near a camera disposed onthe laser tracker. Step 2050 is to reflect light from the retroreflectorback to the laser tracker. Step 2060 is to sense the reflected light.The sensing may be done by a photosensitive array within a cameradisposed on the tracker; by a position detector in the tracker, or by adistance meter within the tracker. Step 2070 is to determine the commandbased on the rule of correspondence. Step 2080 is to execute thecommand.

FIG. 21 shows steps 2100 that are carried out in giving a gesture tocommunicate a command to the laser tracker according to the discussionsthat referenced FIGS. 3D and 5A. Step 2110 is to provide a rule ofcorrespondence between commands and temporal patterns. Step 2120 is forthe user to select a command from among the possible commands. Step 2130is to project a light from the laser tracker to the retroreflector. Thislight may be a beam of light emitted along the optical axis of the lasertracker or it may be light emitted by an LED near a camera disposed onthe laser tracker. Step 2140 is to reflect light from the retroreflectorback to the laser tracker. Step 2150 is to sense the reflected light.The sensing may be done by a photosensitive array within a cameradisposed on the tracker; by a position detector in the tracker, or by adistance meter within the tracker. Step 2160 is for the user to create atemporal pattern in the optical power received by the sensors on thelaser tracker. Such a temporal pattern is easily done by blocking andunblocking a beam of light as discussed hereinbelow. Step 2170 is todetermine the command based on the rule of correspondence. Step 2180 isto execute the command.

FIG. 22 shows steps 2200 that are carried out in giving a gesture tocommunicate a command to a six DOF laser tracker according to thediscussions that referenced FIGS. 3E and 5B. Step 2210 is to provide arule of correspondence between commands and pose of a six DOF target.Step 2220 is for the user to select a command from among the possiblecommands. Step 2230 is to use the six DOF laser tracker to measure atleast one coordinate of a six DOF target in a first pose. A poseincludes three translational coordinates (e.g., x, y, z) and threeorientational coordinates (e.g., roll, pitch, yaw). Step 2240 is for theuser to change at least one of the six dimensions of the pose of the sixDOF target. Step 2250 is to measure the at least one coordinate of asecond pose, which is the pose that results after the user has completedstep 2240. Step 2260 is to determine the command based on the rule ofcorrespondence. Step 2270 is to execute the command.

FIG. 23 shows steps 2300 that are carried out in giving a gesture tocommunicate a command to the laser tracker to point the laser beam fromthe laser tracker to the target and lock onto the target. Step 2310 isto project light onto the retroreflector. This light may be lightemitted by an LED near a camera disposed on the laser tracker. Step 2320is for the user to move the retroreflector in a predefined spatialpattern. Step 2330 is to reflect light from the retroreflector to thelaser tracker. Step 2340 is to sense the reflected light. The sensingmay be done, for example, by a photosensitive array within a cameradisposed on the tracker. Step 2350 is to determine the command based onthe rule of correspondence. Step 2360 is to point the beam of light fromthe tracker to the retroreflector. Step 2370 is to lock onto theretroreflector with the laser beam from the tracker.

FIG. 24 shows steps 2400 that are carried out in giving a gesture tocommunicate a command to the laser tracker to point the laser beam fromthe laser tracker to the target and lock onto the target. Step 2410 isto project light onto the retroreflector. This light may be lightemitted by an LED near a camera disposed on the laser tracker. Step 2420is to reflect light from the retroreflector to the laser tracker. Step2430 is to sense the reflected light. The sensing may be done, forexample, by a photosensitive array within a camera disposed on thetracker. Step 2440 is to generate a predefined temporal pattern, asdiscussed hereinabove. Step 2450 is to determine the command based onthe rule of correspondence. Step 2460 is to point the beam of light fromthe tracker to the retroreflector. Step 2470 is to lock onto theretroreflector with the laser beam from the tracker.

FIG. 25 shows steps 2500 that are carried out in giving a gesture tocommunicate a command to the laser tracker to point the laser beam fromthe laser tracker to the target and lock onto the target. Step 2510 isto project light onto the retroreflector. This light may be lightemitted by an LED near a camera disposed on the laser tracker. Step 2520is to measure at least one coordinate of a first pose of a six DOFtarget. As discussed hereinabove, the pose includes three translationaland three orientational degrees of freedom. Step 2530 is to change atleast one coordinate of a first pose. Step 2540 is to measure the atleast one coordinate of a second pose, which is the pose that resultsafter the at least one coordinate of the six DOF probe has been changed.Step 2550 is to determine the rule of correspondence has been satisfied.Step 2560 is to point the beam of light from the tracker to theretroreflector. Step 2570 is to lock onto the retroreflector with thelaser beam from the tracker.

While preferred embodiments have been shown and described, variousmodifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. Accordingly, it is to beunderstood that the present invention has been described by way ofillustrations and not limitation.

The presently disclosed embodiments are therefore to be considered inall respects as illustrative and not restrictive, the scope of theinvention being indicated by the appended claims, rather than theforegoing description, and all changes which come within the meaning andrange of equivalency of the claims are therefore intended to be embracedtherein.

What is claimed is:
 1. A method for optically communicating, from a userto a laser tracker, a command to control operation of the laser trackerwith steps comprising: providing a rule of correspondence between eachof a plurality of commands and each of a plurality of temporal patterns;selecting by the user a first command from among the plurality ofcommands; projecting a first light from the laser tracker to aretroreflector; reflecting a second light from the retroreflector, thesecond light being a portion of the first light; obtaining first senseddata by sensing a third light imaged onto a photosensitive array, thethird light being a portion of the second light; creating by the user,between a first time and a second time, a first temporal pattern, thefirst temporal pattern including at least a decrease in optical power ofthe third light followed by an increase in the optical power of thethird light, the first temporal pattern corresponding to the firstcommand; determining the first command based at least in part onprocessing the first sensed data according to the rule ofcorrespondence; and executing the first command with the laser tracker.2. The method of claim 1, wherein the step of projecting a first lightfrom the laser tracker to a retroreflector further includes a step ofilluminating a light emitting diode disposed on the laser tracker toproject the first light.
 3. The method of claim 2, wherein the firstcommand includes steps of: pointing a fourth beam of light from thelaser tracker to the retroreflector; and locking onto the retroreflectorwith the fourth beam of light.
 4. A method for optically communicating,from a user to a laser tracker, a command to control operation of thelaser tracker with steps comprising: providing a rule of correspondencebetween each of a plurality of commands and each of a plurality oftemporal patterns; selecting by the user a first command from among theplurality of commands; projecting a first light from the laser trackerto a retroreflector; reflecting a second light from the retroreflector,the second light being a portion of the first light; obtaining firstsensed data by sensing a third light imaged onto a position detector,the third light being a portion of the second light; creating by theuser, between a first time and a second time, a first temporal pattern,the first temporal pattern including at least a decrease in opticalpower of the third light followed by an increase in the optical power ofthe third light, the first temporal pattern corresponding to the firstcommand; determining the first command based at least in part onprocessing the first sensed data according to the rule ofcorrespondence; and executing the first command with the laser tracker.5. A method for optically communicating, from a user to a laser tracker,a command to control operation of the laser tracker with stepscomprising: providing a rule of correspondence between each of aplurality of commands and each of a plurality of temporal patterns;selecting by the user a first command from among the plurality ofcommands; projecting a first light from the laser tracker to aretroreflector; reflecting a second light from the retroreflector, thesecond light being a portion of the first light; obtaining first senseddata by sensing a third light intercepted with a distance meter, thethird light being a portion of the second light; creating by the user,between a first time and a second time, a first temporal pattern, thefirst temporal pattern including at least a decrease in optical power ofthe third light followed by an increase in the optical power of thethird light, the first temporal pattern corresponding to the firstcommand; determining the first command based at least in part onprocessing the first sensed data according to the rule ofcorrespondence; and executing the first command with the laser tracker.